This invention relates to apparatus for generating deflection control signals to be supplied to the horizontal and vertical deflecting plates of a plural pickup-tube television camera and, more particularly, to such apparatus wherein the deflection signals supplied to a respective set of plates may be adjusted substantially independently of the remaining deflection signals. The present invention is particularly advantageous in a color television camera of the type having, for example, red, green and blue pickup-tubes, wherein the deflection of the electron beam in a particular tube may be adjusted substantially independently of the adjustment of the deflection of the electron beam in either of the remaining tubes.
In a typical pickup-tube of a television camera, a target, such as a target formed of photoconductive material, is scanned by an electron beam which forms a raster thereon. The raster generally is of a smaller dimension than that of the target and, for purposes of the present discussion, is referred to as a "frame". The horizontal and longitudinal dimensions of this frame are determined by the horizontal and vertical deflections of the electron beam. In a so-called one-tube camera, such as a monochrome or black-and-white television camera, a single electron beam scans a single raster, or frame, on the target. It is conventional to provide manually operative controls to enable the operator of the camera to effect various adjustments in the characteristics of the frame such as, for example, a centering adjustment which serves to move the geometric center of the frame to a desired location on the target, a size adjustment which serves to change the horizontal and/or vertical dimension of the frame, thus changing its size, a skew or rotation adjustment which serves to rotate the frame about its center portion, and the like. Typically, these adjustments may be effected by the operator to compensate for changes in the operating characteristics of the electronic circuitry due to, for example, temperature, age, and the like. Also, in the event of mechanical changes which might occur, or variations in electrical and mechanical alignment, the capability of such adjustments is desirable.
In some television camera tubes, electromagnetic deflection apparatus is provided for controlling the horizontal and vertical deflection of the beam. The aforementioned adjustments may be achieved by mechanically changing the relative positions of, for example, the deflecting coils. It is difficult to attain precise adjustments in the frame, or raster, merely by relying on mechanical means.
Other television cameras utilize electrostatic deflection plates to achieve the horizontal and vertical deflections of the electron beam. Adjustments in the frame, or raster, in such tubes generally are attained by modifying the deflection voltages which are supplied to the electrostatic deflection plates. For example, the usual horizontal and vertical sawtooth deflection voltage waveforms have adjustment voltages superimposed thereon. While such electronic techniques provide satisfactory adjustments in the raster, difficulties arise when this technique is used in a color television camera of the type having a plurality of pickup-tubes, such as a three-tube (red, green, blue) camera.
In the three-tube color camera, separate deflection apparatus is provided for the respective tubes. For example, a set of horizontal and vertical deflection devices is provided for the red tube, another set of horizontal and vertical deflection devices is provided for the green tube, and a third set of horizontal and vertical deflection devices is provided for the blue tube. A common source generates the sawtooth deflection voltages for all of the horizontal deflection devices, and a common source generates the sawtooth deflection voltages for all of the vertical deflection devices. If adjustments in the rasters are needed, it is not unusual to adjust the sawtooth voltage waveforms generated by the horizontal and vertical deflection voltage sources, such that the same adjusted deflection voltage is applied to all of the horizontal deflection devices and, likewise, the same adjusted vertical deflection voltage is applied to all of the vertical deflection devices.
However, when electrostatic deflection plates are used in such a three-tube color camera, it is possible that mechanical variations may exist between, for example, the deflection plates associated with the red tube and the deflection plates associated with the green or blue tube. As one example thereof, the deflection plates associated with one tube may be larger or smaller than the corresponding deflection plates associated with one or both of the other tubes. As another example, the relative position of the deflection plates associated with one tube may differ from the relative position of the deflection plates associated with one or the other of the remaining tubes. As a result of such mechanical differences between the deflection plates of the various tubes, the raster scanned by, for example, the red tube may differ in size, location or position on the target, relative to the raster scanned by the green and/or blue tubes. This variation in the "red" raster may be adjusted by superimposing the aforementioned adjustment voltages on the horizontal and/or vertical deflection voltages. However, since the same horizontal and vertical deflection voltages are supplied to the horizontal and vertical deflection plates, respectively, of all of the tubes, a correction in the "red" raster may result in an undesired change or distortion, in the "green" and/or "blue" rasters. Because the deflections of the red, green and blue beams cannot be adjusted independently of each other, a proper adjustment in one may deleteriously affect the raster scanned by the others. As a result, distortion, interference, and noise may appear in the color television picture which ultimately is reproduced from the video signals derived from the color camera.